Lubricating oils



United States Patent 3,0?2585 LUBRXCATKNG OKLS Harold D. Orlofi, Oak Park, Mich, assignor to Ethyl Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed July 10, 1959, Ser. No. 826,105 7 Claims. (Cl. ESL-48.4)

This invention relates to improved lubricant compositions which have enhanced resistance to oxidative deterioration at elevated temperatures.

Lubricants, especially petroleum hydrocarbon oils and synthetic oils, undergo oxidative deterioration in service, particularly at elevated temperatures short of the cracking temperature of the particular oil. This deterioration results in the formation of gums and insoluble sludges, the corrosion of metal parts of the equipment with which the oils are used, the loss of useful properties of the oil, and the like. While some antioxidants have been developed which are somewhat effective in inhibiting this deterioration, they had to be used at relatively high concentrations in order to provide effective prolongation of the useful life of the lubricant. Other antioxidants are quite effective at low temperatures but are essentially ineflective when the oil is subjected to drastic oxidizing conditions, such as elevated temperatures and the presence in the oil of metallic substances tending to catalyze its deterioration. The severity of conditions imposed on modern lubricants in the operation of more and more powerful engines and other equipment at higher and higher temperatures has led to the need for the development of improved oils. Single oil compositions are limited by the nature of the material employed as a lubricant, it has been impossible to provide additive free lubricants which can meet these requirements.

It is, therefore, an object of this invention to provide lubricants which have a high degree of resistance to oxidative deterioration, particularly at the high temperatures encountered in the present day equipment. A further and more specific object is to provide petroleum derived hydrocarbon oils normally susceptible to oxidative deterioration containing an effective amount of an inhibitor of such deterioration. A still further object is to provide synthetic lubricants stabilized against oxidative deterioration both during storage and in use at high temperatures. A particular object of this invention is to provide synthetic diester lubricating oils stabilized against oxidative deterioration.

The above and other objects of this invention are accomplished by providing a lubricating oil normally susceptible to oxidative deterioration inhibited against such deterioration by a small antioxidant quantity, up to about percent, of a compound having the formula:

where R is an alkyl radical having from 3 to about 12 carbon atoms and which is branched on the alpha carbon atom and X is a halogen such as chlorine, bromide or iodine. It has been found in practice that small amounts of such a compound very effectively stabilize lubricating compositions such as petroleum hydrocarbon oils, synthetic diester oils and other synthetic oils against oxidative deterioration.

Although concentrations of the 2,2-thiobis-(4-halo-6- alkylphenol) compounds of this invention, up to 5 percent, may be employed, the compounds are such effective stabilizers that concentration ranges of from 0.001 to 3,0h2585 Patented June 1963 "ice about 2 percent by weight are usually suflicient to effectively stabilize an oil (based on the weight of the oil). The most preferred concentration range is from about 0.2 to about 1.5 percent by weight of the additive based on the weight of the oil. Deviations from these concentrations are acceptable and sometimes useful depending upon the initial degree of instability of the lubricant being stabilized and the severity of conditions to which the finished product is to be subjected. Smaller amounts of the compounds may be employed when the lubricant is to be used at lower temperature and oxidation in storage is the primary problem.

The preferred compounds of this invention are those in which the alkyl group designated by R in the above formula is a tertiary alkyl group having from 4 to 8 carbon atoms. These compounds are preferred as they are extremely effective antioxidants. Within this group the most preferred compounds are those in which the alkyl group is a tertiary butyl group. Compounds of this nature have been found to be particularly effective in the inhibition of high temperature oxidation.

Another class of preferred compounds are those in which the halogen atom designated by X in the above formula is a chlorine atom. These compounds are in general more effective than the corresponding bromine and iodine compounds and may be produced inexpensively on a commercial scale. Thus, the most particularly preferred compound of this invention is 2,2'-thi0bis- (4-chloro-6-tert-butylphenol). This compound is preferred because of its outstanding elfectiveness and ease of preparation.

The synthetic lubricants which are enhanced by the practice of this invention are, in general, non-hydrocarbon organic compositions; i.e., organic compositions which contain elements other than carbon and hydrogen. Examples of general classes of material which are protected against oxidative deterioration by the inclusion therein of a 2,2-thiobis-(4-halo-6-alkylphenol) of this invention include diester lubricants, silicones, halogen "containing organic compounds including the fluorocarbons', polyalkylene glycol lubricants, and organic phosphates which are suitable as hydraulic fluids and lubricants. Excellent results are obtained when a 2,2'-thiobis- (4-halo-6-branched alkylphenol) is added to any member of these classes of materials; however, it has been found that exceptional oxidative stability is imparted to diester lubricants by the practice of this invention. Thus a synthetic diester lubricant containing from about 0.001 to about 2 percent by weight of 2,2-thiobis-(4-halo-6- branched alkylphenol) constitutes a preferred embodiment of this invention. The synthetic diester oil or stabilized by the practice of this invention include sebacates, adipates, etc., which fined particular use as aircraft instrument oils, hydraulic and damping fluids, and precision bearing lubricants. These diester oils are exceedingly difiicult to stabilize under high temperature conditions. In this invention, use can be made of a wide variety of diester oils of the type described in Industrial and Engineering Chemistry, 39, 484-91 (1947). Thus, use can be made of the diesters formed by the esterification of straight chain dibasic acids containing from 4 to about 16 carbon atoms with saturated aliphatic monohydric alcohols containing from 1 to about 10 carbon atoms. Of these diester toils, it is preferable that the alcohol used in their preparation be a branched chain alcohol because the resultant diestens have very valuable lubricating properties and the inhibitor of this invention very effectively stabilizes these materials against oxidative deterioration. Thus, use can be made of oxalates, malona-tes, succinates, glutarates, adipates, pimelates, suberates, azelates, sebacates, etc.

o a The diester lubricants used in the lubricant compositions of this invention have the formula:

COORi cooni where R is an aliphatic hydrocarbon radical which may be saturated or unsaturated and has from 2 to 14 carbon atoms and R and R are straight or branched chain alkyl groups. The diesters utilized in the preferred lubricant compositions include esters of succinic, glutaric, adipic, pimelic, suberic, azelaic and sebacic acid. Typical examples of such esters are diisooctyl azelate, di-(2-ethylhexyl) sebacate, di-sec-amyl sebacate, diisooctyl adipate, di-(Z-ethylhexyl) adipate, di-(Z-ethylhexyl) azelate, di- (l-methyl-4-ethyloctyl) glutarate, diisoarnyl adipate, di- (Z-ethylhexyl) glutarate, di-(Z-ethylbutyl) adipate, ditetradecyl sebacate and di-(Z-ethylhexyl) pinate.

The preferred diesters are generally prepared by esterifying one mole of a dicarboxylic acid having the general formula: HOOC(CH COOH, where x is an integer of from 2 to 8, with 2 moles of a branched chain alcohol containing at least 4 carbon atoms. Typical are the reactions of succinic, glutaric, adipic, pimelic, suberic or azelaic acid with sec-amyl alcohol, 3-ethyl butanol, 2- ethyl hexanol or the branched chain secondary alcohols undecanol or tetradecanol.

The preferred diester lubricant fluids have molecular weights ranging from about 300 to about 600 and freezing and pour points from about -40 to less than about 100 F. Their flash and fire points range from about 300 F. to about 500 F. and their spontaneous ignition temperatures range from about 100 to about 800 F. The diesters made by reacting a dicarboxylic acid with a branched chain alcohol have been found to have superior viscometric properties as compared with diesters made by reacting dihydric alcohols with mono-carboxylic acids and thus, diesters prepared by the former method are preferred in formulating the lubricant compositions of this invention.

The diester oils may be formed by the reaction of a polycarboxylic acid with a mono-hydric alcohol, the reaction of a polyhydric alcohol with a mono-carboxylic acid, reaction between a polyhydric alcohol with a polycarboxylic acid, or combinations of the above reactions; for example, reaction of a polycarboxylic acid with a glycol and a mono-hydric alcohol, reaction of a glycol with a polycarboxylic acid and a mono-carboxylic acid, or the reaction of a glycol, a mono-hydric alcohol, a polycarboxylic acid and a mono-carboxylic acid. The acids may be mono-carboxylic aliphatic acids such as, propionic acid, valeric acid, 2-ethyl enanthic acid, 2,2-dipropyl butyric acid or 3-(2-methylhexyl) valeric acid. They may contain unsaturated linkages as in senecioic acid, sorbic acid, or angelic acid; they may be polycarboxylic aliphatic acids such as succinic acid, glutaric acid, azelaic acid, -octene- 1,8-dicarboxylic acid, or 3- leXane-Z,3,4-tricarboxylic acid, and they may be aromatic or cycloaliphatic acids, such as cyclohexane acetic acid, 1,4-cyclopentylenebis acetic acid, phthalic acid, hemimellitic acid, and terephthalic acid.

The alcohols used in preparing the polyester lubricant base materials may be aliphatic mono-hydric alcohols such as propanol, 2-ethyl-3-hexenol, 2-ethyl-4-propyl heptanol, Z-butenol, or Z-methyl propanol. They may be polyhydric aliphatic alcohols, such as 1,6-hexamethylene glycol, 1,10-decamethylene glycol, 2-hexene-1,6-diol, and 1,6- heptylene glycol; and they may be mono or polyhydric alicyclic or aromatic alcohols, such as 4-[m-(2-hydroxyethyl)phenyl]butanol, 3-(2-hydroxyethyl) cyclohexanebutanol, p-(hydroxymethyl) phenethyl alcohol, a-methyl-pxylene-a,a'-diol, 1,4-cyclohexane-a,a-diethyl dimethanol, 2,3-bis-(4-hydroxybutyl) benzyl alcohol, 4,4'-[3-(3-hydroxyhexyl -o-phenylene] dibutanol, and 5- 3- 3-hydroxypropyl cyclopenta-2,4-dienylene] -3 -ethyl amyl alcohol.

Another class of synthetic lubricants which achieve enhanced oxidative stability by the practice of this invention includes the silicone lubricants. The term silicone as used herein is defined as a synthetic compound containing silicon and organic groups. In naming specific compounds, the nomenclature system recommended by the American Chemical Society Committee on Nomenclature, Spelling, and Pronunciation (Chem. Eng. News, 24, 1233 (1946)), will be used. Thus, the compounds which have the SiOfii linkages are the siloxanes. Derivatives of silane, SiI-I in which one or more of the hydrogens in silane are replaced with organic groups are termed the silanes. Silicates and silicate ester compounds are named as oxy derivatives of silane and are called alkoxy or aryloxy silanes.

The silicone oils and greases serving as the base medium for the lubricant compositions of the invention include the polysiloxane oils and greases of the type, polyalkyl-, polyaryl-, polyalkoxy-, and polyaryloXy-, such as polydimethyl siloxane, polymethylphenyl siloxane, and polymethoxyphenoxy siloxane. Further included are silicate ester oils, such as tetraalkyloxy and tetraaryloxy silanes of the tetra-Z-ethylhexyl and tetra-p-tert-butylphenyl types, and the silanes. Also included are the halogen-substituted siloXanes such as the chlorophenylpolysiloxanes.

The polyalkyl, polyaryl, and polyalkyl polyaryl siloxanes are the preferred types of base medium for the silicon containing lubricant compositions of the invention b cause of their high oxidative stability over a wide temperature range. The polyalkyl siloxanes, such as the dimethyl polysiloxane, are slightly preferred over the polyaryl and polyalkyl polyaryl siloxanes because they show the least change in viscosity over a wide temperature range.

Certain halogen containing organic compounds have physical properties which render them particularly well suited as lubricants. Ordinarily, the halogen is either chlorine or fluorine. Typical of the chlorinated organic compounds suitable as lubricants are the chlorodiphenyls, chloronaphthalene, chlorodiphenyl oxids and chloronated parafiin waxes.

The fluorocarbon lubricants which are enhanced by this invention are linear polymers built up of a recurring unit which is The fluorocarbon oils and greases are very stable chemically and have high thermal stability. These desirable physical properties appear to be closely related to the bond distances occurring in the fluorocarbon polymeric molecule, which may also contain chlorine bonded to carbon.

Polyalkylene glycol lubricants which are benefited by the practice of this invention are ordinarily the reaction product of an aliphatic alcohol with an alkylene oxide. The preferred alkylene oxides are ethylene oxide and propylene oXide. Depending upon the alcohol employed and the molecular weight of the compound, the polyalkylene glycol lubricants may be either water insoluble or Water soluble. The molecular weights of these polymers may vary from about 400 to over 3,000. In general, the polyalkylene glycol lubricants are characterized by high viscosity indices, low API gravities, low pour points and they have the general formula where n is small integer and depends upon the alkylene oxide employed and x is a large integer from about 10 to about depending upon the molecular Weight of the finished lubricant and R represents the hydrocarbon group derived from the particular aliphatic alcohol employed.

Another important class of synthetic materials which are enhanced by the practice of this invention are phosphate esters which are, in general, prepared by the reaction of an organic alcohol with phosphoric acid and have the general formula:

where R, R and R" represent either hydrogen or an organic radical and where at least one of the groups repre sented by R, R and R" is an organic radical. Typical of these materials is tricresylphosphate. The phosphate esters are in general characterized by excellent fire resistant properties and high lubricity. However, their thermal stability is such that they are ordinarily unsuited for high temperature applications above about 300 F. Other examples of phosphate esters include: Tris-(Z-chloro-lmethylethyl)phosphate; tri-n-butyl-phosphate; tris-(Z-ethy1hexyl)phosphate; triphenyl phosphate; tris-(p-chlorophenyl)phosphate; diethyl m-tolyl phosphate; p-chloro phenyl dimethyl phosphate; tris-(2-n-butoxyethyl)phosphate; dimethyl m-tolyl phosphate; di-n-propyl-m-tolyl phosphate; di-n-butyl phenyl phosphate; 1,3-butylene flchloroisopropyl phosphate; methyl di-m-tolyl phosphate; bis-(2-ch1oro-1-methylethyl) m-tolyl phosphate; dimethyl 3,5-xylyl phosphate; 4-chloro-m-tolyl dimethyl phosphate; 2-ethyl-l-n-propyl trimethylene methyl phosphate; 4- chloro-m-tolyl l-methyltrirnethylene phosphate; dimethyl n-octyl phosphate, and the like.

The mineral lubricating oils which are greatly benefited by the practice of this invention are those derived from naturally occurring petroleum crude by distillation and various other refining processes well known in the art. These oils include lubricating and industrial oils such as crankcase lubricating oils, transformer oils, turbine oils, transmission fluids, cutting oils, gear oils, industrial oils, mineral white oils, glass annealing oils, oils thickened with soaps and inorganic thickening agents (greases) and in general, engine and industrial oils which are derived from crude petroleum and are normally susceptible to deterioration in the presence of air, particularly at elevated temperatures and most particularly in the presence of metal containing catalysts such as iron, iron oxide, copper and silver.

The greases used in formulating lubricant compositions of the invention are formed by admixing a soap with an oil of any of the types described above. Such soaps are derived from animal or vegetable fats or fatty acids, wool grease; rosin, or petroleum acids. Typical examples are lead oleate, lithium stearate, aluminum tn'stearate, calcium glycerides, sodium oleate and the like. In addition, the polyester greases may contain unreaoted fat, fatty acids and alkali; unsaponifiable matter including glycerol and fatty alcohols; rosin or Wool grease; Water; and certain additives which may function as modifiers or peptizers.

In formulating the grease compositions of this invention, greases prepared by admixing a lithium soap with the polyester oils are preferred as they have superior oxidative stability as compared with greases formulated with other soaps, such as the sodium, calcium or lead soaps.

In preparing the improved lubricant compositions of this invention, an appropriate quantity of 2,2-thiobis-(4-halo- G-branched alkylphenol) is blended with the lubricant to be stabilized. If desired, preformed concentrated solutions of the stabilizer in the base lubricant can be prepared and then subsequently diluted with additional lubricant to the desired concentration. An advantage of this invention is the fact that 2,2-thiobis-(4-chloro-6-tert-butylphenol) is easily and rapidly blended with the base oil and because of the relative low melting point of the stabilizer, there is no danger of separation of the stabilizer from the lubricant under normal use conditions. An additional advantage of this invention is that 2,2-thiobis-(4- chloro-o-tert-butylphenol) is highly compatible with the usual additives that are frequently used to fortify lubricant compositions such as detergent-dispersants, viscosity 6 index improvers, dyes, anti-rust additives, anti-foaming agents, and the like.

The following examples illustrate various specific embodiments of this invention. The physical characteristics of the illustrative hydrocarbon oils used in the examples are shown in Table I.

TABLE I.PROPERTIES OF REPRESENTATIVE PETROLEUM HYDROCARBON OILS Oil A B C D E F Gravity at 60 API 30. 3 30. 5 28. 8 31. 1 20. 5 31. 0 Viscosity, Saybolt:

Seconds at F 178. 8 373. 8 309. 8 169. 0 249. 4 335. 4

Seconds at 210 F 52. 0 58. 4 63. 8 51. 5 45. 7 68. 4 Viscosity Index 157.8 144. 4 Pour Point-.. 0 Flash Point- 385 Sulfur, Percen 0. 1

Example 1 To 100,000 parts of Oil A is added with stirring 12 parts (0.012 percent) of 2,2 thiobis-(4-chloro-6-tert-butylphenol). The resulting oil is found to possess improved resistance to oxidative deterioration.

Example 2 To 100,000 parts of Oil B is added 2,000 parts (2 percent) of 2,2-thiobis-(4-bromo-6-sec-dodecylphenol). On agitating this mixture, a homogeneous solution results and the resulting oil composition possesses enhanced oxidation resistance.

Example 3 With 100,000 parts of Oil C is blended 50 pants (0.05 percent) of 2,2-thiobis- [4-iodo-6-( 1, 1,3,3-tetramethylbutyl)phenol]. The resulting oil possesses enhanced resistance against oxidative deterioration.

Example 4 To 100,000 parts of Oil D is added 100 parts (0.1 percent) of 2,2-thiobis-(4-bromo-6-tert-butylphenol). The resulting oil is found to possess enhanced resistance against oxidative deterioration.

Example 5 With 100,000 parts of Oil E is blended 5 parts (0.005 percent) of 2,2 thiobis (4-chloro-6-isopropylphenol). After mixing the resulting oil possesses enhanced resistance to oxidation.

Example 6 To 100,000 parts of Oil F is added parts (0.15 percent) of 2,2-thiobis-(4-bromo-G-tert-amylphenol.) The resulting oil possesses enhanced resistance against oxidative deterioration.

Example 7 To 100,000 parts of di-(Z-ethylhexyl) sebacate having a viscosity at 210 F. of 37.3 SUS, a viscosity index of 152 and a molecular weight of 426.7 is added 1 part (0.001 percent) of 2,2-thiobis-(4-iodo-6-tert-butylphenol). After mixing, the resultant diester lubricant possesses greatly enhanced oxidation resistance.

Example 9 To 100,000 parts of di-(Z-ethylhexyl) adipate having a viscosity at 210 F. of 34.2 SUS, a viscosity index of 121 and a molecular weight of 370.6 is added 5,000 parts (5 percent) of 2,2 thiobis (4-chloroG-tert-butylphenol) After mixing, the resultant diester lubricant possesses out standing resistance against oxidative deterioration.

Example 10 Five parts of 2,2'-thiobis-(4-chloro-6-tert-octylphenol) are blended with 2,495 parts of diisooctyl azelate having a kinematic viscosity of 3.34 centistokes at 65 F. (ASTM 445-52T), an ASTM slope from 40 F. to 210 F. of 0.693 (ASTM D341-43) and a pour point of -85 F. (ASTM D97-47). Its flash point is 425 F. (ASTM D92-52), and its specific gravity is 0.9123 at 25 C. The resulting lubricant is extremely stable to oxidation.

Example 11 Three parts of 2,2-thiobis-(4chloro-6-tert-butylphenol) are blended and mixed with 197 parts of a grease comprising 12.5 percent of lithium stearate, 1 part of polybutene (12,000 molecular weight), 2 percent of calcium xylyl stearate and 84.5 percent of di-(Z-ethylhexyl) sebacate, to prepare an improved grease of this invention.

Example 12 One part of 2,2'-thiobis-(4-bromo-6-tert-butylphenol) is blended with 75 parts of diisooctyl adipate having a visco ity of 35.4 SUS at 210 F., a viscosity of 57.3 SUS at 100 F., a viscosity of 3,980 SUS at 40 F. and a viscosity of 22,500 at -65 F. Its viscosity index is 143, its AST M pour point is below -80 F. and its specific gravity (60 F./60 F.) is 0.926.

Example 13 An improved stable grease of this invention is prepared by blending 8 parts of 2,2'-thiobis-(4-chloro-6-tertbutylphenol) with 920 parts of grease comprising 12 percent of lithium stearate, 1 percent of polybutene (12,000 molecular weight), 2 percent of calcium xylyl stearate, 34.0 percent of di-(Z-ethylhexyl) sebacate and 51 percent of di-(Z-ethylhexyl) adipate.

Example 14 Ten parts of 2,2-thiobis-(4-chloro-6-isopropylphenol) are mixed with 10,000 parts of a grease comprising 11 percent of lithium stearate, 1 percent of polybutene (12.000 molecular weight), 1 percent of sorbitan monooleate. 86.6 percent of di-[1-(2-methylpropyl)-4-ethyloctyl]sebacate.

Example 15 Two parts of 2,2-thiobis-(4-iodo-6-sec-butylphenol) are blended with 100 parts of a polymethylpolyphenyl siloxane grease of medium weight consistency having a penetration of 240 280 (ASTM 2l748), a minimum melting point of 400 F. and a serviceable temperature range of from 30 to 400 F. (This siloxane grease is sold under the trade name Dow-Corning 44.)

Example 1 6 To a siloxane fluid having a viscosity of 71 centistokes at 25 C. and 24 centistokes at 75 C., a specific gravity of 1.03 at 25 C., a freezing point of 70 C. and a flash point of 540 R, which is composed of a halogen substituted polyphenylpolymethyl siloxane is added suflicient 2.2-thiobis-(4-chloro-6-tert-butylphenol) to give a composition containing 1.5 percent of the additive. This oil has an extremely high degree of resistance against oxidative deterioration due to the presence of the 2,2-thiobis-(4-chloro-6-tert-butylphenol).

Example 17 To a phenylmethyl polysiloxane fluid having a viscosity of 100-150 centistokes at 25 C., an open cup flash point of 575 F. (ASTM D9233), a freezing point of 60 F., and a specific gravity of 1.07 at 77 F. is added suflicient 2.2 thiobis-[4-chloro-6-(l,1,3,3-tetrarncthylamyl) phenol] to give a composition containing 0.1 percent of the additive.

Example 18 Ten parts of 2,2'-thiobis-(4-bromo-6-tert-butylphenol) are blended with about 1,000 parts of monoethyl diethoxy monoacetoxy silan (boiling point 191.5 C.) to prepare an enhanced oil of this invention.

Example 19 A one percent solution of 2,2-thiobis-(4'chloro-6-tertbutylphenol) in tribenzyl-n-hexadecyl silane (boiling point 245248 C.) constitutes an improved lubricant within the scope of this invention.

Example 20 To a poly(trifluorochloroethylene) having the formula (CF CFCD and an average molecular weight of 880, pour point of 5 C. and a viscosity of 45 centistokes at 160 F. is added 1.25 percent of 2,2-thiobis-(4-iodo-6- sec-heptylphenol) to prepare an improved lubricant of this invention.

Example 21 A composition consisting of 0.01 percent of 2,2-thiobis-(4-chloro-6-tert-butylphenol) is prepared by blending an appropriate quantity of the compound with a fluorocarbon grease having a penetration of 267 millimeters at 77 F., 285 millimeters at F. and 300 millimeters at F. (ASTM 217-48); and a dropping point of at least 400 F. (ASTM D566 42). This grease is commercially available under the tread name Fluorolube GR-544.

Example 22 To a polyalkylene glycol oil lubricant having a viscosity index of 148, ASTM pour point of 55 F., a flash point of 300 F., a specific gravity of 0.979 and a Saybolt viscosity of at 100 F. is added 1 percent of 2,2- thiobis-(4-chloro-6-tert-butylphenol) to prepare an extremely oxidation resistant polyalkylene glycol lubricant.

Example 23 A composition containing 0.2 percent of 2,2-thiobis- [4-bromo-6-(2-decyl)phenol] is prepared by adding an appropriate quantity of the compound to a polyalkylene glycol lubricant which is insoluble in water and which has a Saybolt viscosity of 62.7 at 200 F., a viscosity index of 146, ASTM pour point of 40 F., a fire point of 490 F. and a specific gravity of 0.991.

Example 24 An improved lubricant of this invention comprising a chloronated organic compound is prepared by admixing 0.5 percent of 2,2'-thiobis-[4-chlor0-6-(3-nonyl)phenol] with a chlorodiphenyl oil having a distillation range of from 554 to 617 F., a Saybolt viscosity at 100 F. of about 49, a pour point of 30 F. and a specific gravity of about 1.267.

Example 25 An improved hydraulic fluid and lubricant according to this invention is prepared by adding 2 percent of 2,2- thiobis-(4-chloro-6-tert-butylphenol) to tricrecyl phosphate.

To illustrate the outstanding advantages achieved by the practice of this invention, particularly when the compositions are subjected to elevated temperature, runs were conducted using the panel coker test. This test measures the oxidative stability of oils which are maintained at elevated temperatures in the presence of air, the oils periodically coming in contact with a hot metal surface. This test is described in the Aeronautical Standards of the Departments of Navy and Air Force, Spec. MIL-L- 7808C, dated November 2, 1955. In these experiments, the diester lubricant was a commercially available di- (Z-ethylhexyl) sebacate which was devoid of additives. The test was modified so that the panel coker apparatus was operated at 600 F. for 10 hours on a cycling schedule-the splasher being in operation for 5 seconds followed by a quiescent period of 55 seconds. On completion of these tests the extent by which the various test oils were decomposed under these high temperature oxidizing conditions was determined by weighing the amount of deposits which formed on the metallic panel. Under these test conditions, the use of the additive free (ii-(2- ethylhexyl) sebacate caused the formation of 138 milligrams of deposits on the metallic panel. However, the presence of only 0.5 percent by weight of 2,2-thiobis-(4- chloro-6-tert-butylphenol) caused a reduction in panel deposit to 6 milligrams. It is seen, therefore, that 2,2- thiobis-(4-chloro-6-tert-btuylphenol) provides outstanding resistance to oxidative deterioration when employed as an additive to diester oils.

To further demonstrate the benefits resulting from the practice of this invention, additional panel coker tests were carried out using petroleum hydrocarbon lubricating oil. The test conditions were identical with those above except that the temperature of the lubricants was maintained at 550 F. The base oil used was an initially additive-free solvent-refined commercial neutral mineral lubricating oil having a viscosity at 100 F. of 200 SUS and a viscosity index of 95. It was found that the additive free oil formed 434 milligrams of deposit on the panel when subjected to the foregoing tests conditions. However, When the oil had been treated with one percent by weight of 2,2-thiobis-(4-chloro-6-tert-butylphenol), there were only 16 milligrams of deposit on the panel, amounting to a reduction in panel deposits of over 96 percent.

To further illustrate the effectiveness of the 2,2'-thiobis-(4-halo-6-alkylphenol) compounds as lubricant additives, tests were conducted on a highly refined mineral derived oil having a viscosity index of 106.5 and -a viscosity of 87.1 SUS at 100 F. The oil was charged in separate samples (with and without an additive of this invention) to an apparatus for measuring the oxidative stability of the oil. The apparatus consists of a glass vessel having a 12 milliliter capacity and an inlet tube which can be connected to a mercury manometer. After the oil is charged, the vessel is flushed with oxygen at atmospheric pressure and then connected to the mercury manometer. The vessel is then immersed in a constant temperature bath at 150 C. whereupon changes in the oxygen pressure are indicated on the manometer. The manometer is observed until a rapid pressure drop in the vessel occurs. The time from immersion to the initiation of the pressure drop is the induction period of the oil. To all samples, ferric hexoate is added to catalyze oxidation and make the test more severe. The concentration of the iron salt is adjusted to 0.05 percent based on Fe O One milliliter of the oil is charged to the apparatus in each test. In tests of this nature the base oil has an induction period of from 2 to 3 minutes, showing that it is completely unstable to oxidative deterioration at 150 C. However, when the oil contained 1.0 moles per liter of 2,2-thiobis-(4-chlo1'o-6-tert-butylphenol), the induction time was 1095 minutes. Thus the stability of the oil was raised by the enormous factor of about 360- 550 times its original value.

Another illustration of the improvements in oil stability achieved by the practice of this invention are shown by Polyveriform Oxidation Stability Tests, described in the paper entitled Factors Causing Lubricating Oil Deter1oration in Engines (Industrial and Engineering Chemistry, Analytical Edition, 17, 302, (1945)). See also A Bearing Corrosion Test for Lubricating Oils and its Correlation with Engine Performance (Analytical Chemistry, 21, 737, (1949)). This test effectively evaluates the performance of lubricating oil antioxidants. The test equipment and procedure employed and correlations of the results with engine performance are discussed in the first paper above mentioned.

The amount of oxidation taking place during the test is measured in terms of acid number and viscosity increase of the oil. By contrasting a composition of this invention with a similar oil not containing an additive of this invention, the outstanding benefits are illustrated. For example, in a set of tests conducted as described in the first reference cited above, modified to the extent that the steel sleeve and copper test piece described in the publication were omitted, a non-additive lubricating oil was compared with the same oil containing 0.5 weight percent of the preferred compound of this invention, 2,2- thiobis-(4-chloro-6-tert butylphenol). In order to make the test as severe as possible 70 liters of air per hour were passed through the oil for a period of 20 hours while the oil temperature was maintained at 300 F. The nonadditive oil had an acid number of 6.0 after completion of the test and its viscosity had increased by 103 percent. In distinction to this the sample of oil containing 0.5 weight percent of 2,2-thiobis-(4-chloro-6-tert-butylphenol) had an acid number of only 1.3 and had sufiered only a one percent increase in viscosity during the test. In addition to this, considerably less sludge had formed in the oil of this invention.

To still further illustrate the benefits derived from this invention tests were conducted on an electromotive diesel oil having a viscosity index of 54 and a viscosity of 919 Saybolt Universal seconds at F. In this test the oil is heated at 325 F. with agitation for hours. Two metal catalysts are employed to promote degradation of the oil, namely, a silver plated wrist pin bushing specimen and a copper metal catalyst specimen. Degradation of the oil is determined by acid number after the test and percent viscosity increase at 100 F. In addition the condition of the silver bushing is established by determining the weight change during the test. A decrease in the weight of the silver specimen indicates poor performance in the oil. One sample of the oil employed in this test contained a commercially available zinc dithiosulfate in amount equivalent to 0.02 weight percent phosphorus. In this test the acid number of the oil increased to 2.6 and there was a 47 percent increase in the viscosity. However, when an oil containing 4 percent of a barium sulfonate and 0.35 percent by weight of 2,2'-thiobis-(4-methyl-6-tert-butylphenol) was subjected to the test, the final acid number was only 0.9 and the viscosity had increased only 40 percent. In addition the silver test specimen came through the test essentially unchanged.

In the compositions of this invention effective use can be made of other additives which are known to the art, such as other inhibitors, detergent-dispersants, pour point depressants, viscosity index improvers, anti-foam agents, rust inhibitors, oiliness or film strength agents, dyes and the like. Of the inhibitors which can be effectively used in combination with the additives of this invention are sulfurized sperm oil, s-ulfurized terpenes, sulfurized parafiin Wax olefins, aromatic sulfides, alkyl phenol sulfides, lecithin, neutralized dithio-phosphates, phosphorus pentasulfide-terpene reaction products, diphenylamine, phenylnaphthyl amine, fi-naphthol, pyrogallol, and the like. Typical of the detergent additives that can be used in the compositions of this invention are metallic soaps of high molecular weight acids, such as aluminum naphtheuates, calcium phenyl stearates, calcium alkyl salicylates, alkaline earth metal petroleum sulfonates, alkaline earth metal alkyl phenol sulfides (barium amyl phenol sulfide, calcium octyl phenol disulfide, etc), metal salts of wax-substituted phenol derivatives and the like. Of the viscosity index improvers and pour point depressants, effective use can be made of polymers of the esters of methacrylic acids and higher fatty alcohols and the corresponding polymers of esters of acrylic acid and higher fatty alcohols. These and other additives which can be employed in the compositions of this invention will now be well known to those skilled in the art.

The 2,2'-thiobis-(4-chloro-6-alkylphenol) compounds are prepared by the reaction of the corresponding 2-alkyl- 4-halophenol with a sulfur chloride. Thus, 2,2-thiobisii (4-chloro-6-tert-butylphenol) is prepared by the reaction of sulfur dichloride and 2-tert-butyl-4-chlorophenol. This preparation is illustrated by the following examples.

Example 26 A solution of 370 parts of 4-chloro-6-tert-butylphenol and 79 parts of n-hexane was stirred at iii-20 and onehalf of a solution of 10.3 parts of sulfur dichloride and 198 parts of n-hexane was added over a 20 minute peroid. After stirring for one hour the remainder of the sulfur dichloride was added over another 20 minute period. The agitation was continued for 2 /2 hours while the temperature was controlled at 22-25 C. During the agitation of sulfur dichloride, hydrogen chloride gas was evolved. The reaction was stirred overnight and then heated for a /2 hour period at 35 C. The solvent was removed by distillation and the residue then distilled at one milliliter pressure for 100 C. The residue from this distillation was recrystallized from isooctane giving 19 parts of pure 2,2-thiobis-(4-chloro-o-tert-butylphenol) having a melting point of 110111.

Example 27 Following the general procedure of Example 26, 4- bromo-6-(2-dodecyl) phenol is reacted with sulfur dichloride to produce a good yield of 2,2-thiobis-[4-bromo-6- (2-dodecyl)phenol]. One mole of the sulfur dichloride is employed for each mole of the phenol in this reaction. Sufiicient solvent is employed to insure a mobile reaction mass which may be agitated. The temperature is controlled so that the maximum temperature of 30 is obtained during addition of the sulfur dichloride and a maximum of 40 C. is attained during the post-addition cook period.

Example 28 Two moles of 4-iodo-6-isopropylphenol are reacted with one mole of sulfur dichloride at a maximum temperature of 30 C. The sulfur dichloride in n-hexane solution is added to the phenol which is also dissolved in hexane to insure maintenance of the proper temperature. The product is recovered as described in Example 26 above and the reaction results in a high yield of 2,2-thiobis-(4- iodo-6-isopr-opylphenol).

I claim:

1. A lubricating composition comprising a major proportion of a liquid lubricating oil normally susceptible to oxidative deterioration inhibited against such deterioration by a small antioxidant quantity, from 0.001 up to about percent, of a compound having the formula:

OH OH 12 where R is an alkyl radical having from 3 to about 12 carbon atoms and which is branched on the alpha carbon atom, and X is halogen.

2. The lubricating composition of claim 1 wherein said alkyl group is a tertiary alkyl group having from 4 to 8 carbon atoms.

3. The lubricating composition of claim 1 wherein said halogen is chlorine.

4. The lubricating composition of claim 1 wherein said alkyl group is a tertiary butyl group and said halogen is chlorine.

5. A lubricating composition comprising a major proportion of a mineral hydrocarbon lubricating oil and a small antioxidant quantity, from 0.001 to about 2 percent, of 2,2-thiobis-(4-chloro-6-tert-butylphenol).

6. A new composition consisting essentially of a nonhydrocarbon synthetic liquid lubricant, normally susceptible to oxidative deterioration inhibited against such deterioration by the inclusion therein of from 0.001 to about 5 percent by weight of a compound having the formula:

OH OH I X X where R is an alkyl radical having from 3 to about 12 carbon atoms and which is branched on the alpha carbon atom and X is halogen.

7. The lubricating composition of claim 6 wherein said non-hydrocarbon synthetic liquid lubricant is a diester lubricant formed by the esterification of a straghtchain dibasic acid containing from 4 to about 16 carbon atoms with a saturated aliphatic monohydric alcohol containing from 1 to about 10 carbon atoms and wherein said compound is 2,2-thiobis-(4-chloro-6-tert-butylphenol).

References Cited in the file of this patent UNITED STATES PATENTS 2,776,998 Downey Jan. 8, 1957 2,814,597 Wenners et al. Nov. 26, 1957 2,937,208 Retter et al. May 17, 1960 FOREIGN PATENTS 201,160 Australia Jan. 11, 1956 448,017 Canada Apr. 20, 1948 OTHER REFERENCES Morawetz: Phenolic Antioxidants for Paraffinic Materials, I. and E. Chem, vol. 41, No. 7, July 1949, pp. 1442-1447.

Atkins et al.: I. and E. Chem, vol. 39, No. 4, April 1947, pp. 491-497. 

1. A LUBRICATING COMPOSITION COMPRISING A MAJOR PROPORTION OF A LIQUID LUBRICATING OIL NORMALLY SUSCEPTIBLE TO OXIDATIVE DETERIORATION INHIBITED AGAINST SUCH DETERIORATION BY A SMAALL ANTIOXIDANT QUANTITY, FROM 0.001 UP TO ABOUT 5 PERCENT, OF A COMPOUND HAVING THE FORMULA: 